The present invention relates to an apparatus for preventing pipe buckling when downwardly directed axial forces are applied to a pipeline which extends from a derrick down into a well bore, especially when snubbing.
Snubbing is carried out when a drill pipe or production tubing must be forced down into the well against well pressure, and the well pressure is so great that the pipe does not run down by virtue of its own weight. A axial force is then applied to the pipe, forcing the pipe down against well pressure. During snubbing of this kind there is a danger that the pipe might buckle sideways halfway between the top drive, which holds the pipe at its upper end, and the drill deck. The buckling may be so great that the pipe breaks.
In the case of a pipeline consisting of pipes having a diameter of 27/8" (7.3 cm), the buckling length during snubbing is about 70 cm. This means that the pipe must be gripped at intervals of 70 cm in order to apply an axial force. In the case of a pipe length in the derrick, between the drill deck and the top drive, of a total of 9 m, this means that the pipe must be gripped about 13 times to prevent the pipe from breaking. Of course, this takes considerably longer than it would had it been possible to run down the whole pipe length in the derrick at one go.